1. Field of the Invention
The present invention relates to a transparent carbon nanotube (“CNT”) electrode comprising a net-like CNT thin film and a method for preparing the same. More specifically, the present invention relates to a transparent CNT electrode having excellent conductive properties and light transmission properties, comprising a transparent substrate and a net-like CNT thin film formed on the transparent substrate, and a method for preparing the same.
2. Description of the Related Art
Transparent electrodes consisting of a transparent substrate and a conductive film formed on the transparent substrate are now widely used to fabricate a variety of electronic devices, including image sensors, solar cells, liquid crystal displays, organic electroluminescence (“EL”) displays, and touch screen panels, that are required to have both light transmission properties and conductive properties.
Indium tin oxide (“ITO”) electrodes have been predominantly used as electrodes for transparent substrates because ITO readily forms a thin film on glass substrates and exhibits excellent light transmission properties and conductive properties. Vacuum deposition equipment is generally used to produce ITO electrodes. In particular, sputtering equipment is used in view of the excellent characteristics of transparent ITO films prepared by this method. Use of sputtering techniques, however, requires that transparent electrodes be produced at a high processing temperature, typically 200° C. or higher, sometimes 400° C. or higher. Therefore, sputtering techniques are not suitable for the production of flexible displays using transparent electrodes. Moreover, the ITO electrodes are rigid (i.e., inflexible), and when used to prepare flexible displays causes undesirably increased sheet resistance and poor durability of the flexible displays.
To solve these problems, research is actively underway on preparation of transparent carbon nanotube (CNT) electrodes, which use CNTs having high electrical conductivity as materials to form electrode films on transparent substrates. For example, a CNT transparent electrode can be formed from a dispersion of CNTs spray coated on a substrate. However, electrode films prepared using such a method suffers in that significant loss of CNTs results, and there are limitations on electrode films prepared using such methods that are associated with difficulty in controlling film thickness at nanometer scale. As such, formation of the transparent electrode using a dispersion of CNTs in suitable media is required to maintain optical transmissivity of the resulting thin film transparent electrode. Various attempts to prepare the transparent electrode have been made by dispersing the CNTs using dispersants. However, most of the dispersants are composed of organic materials which when incorporated into the transparent electrode can act as insulators, thereby presenting problems associated with poor conductivity of the transparent electrode upon formation of CNTs into a CNT thin film.